I provide some considerations on scientific thought experiments, focusing on their epistemic value. First, I outline the distinctive features of scientific thought experiments, provide some historical background and, as an illustration, describe two thought experiments: Galileo's on falling bodies and Stevin's on inclined plane. I take thought experiments in physics as an example from which more general conclusions can be drawn - about thought experiments in other natural sciences, but also in philosophy, mathematics, and other sciences. Further, I present Kuhn's epistemic puzzle as well as some proposed solutions. This closely relates to the question what kind of processes are involved in scientific thought experimenting. The satisfactory answer must consider scientific discoveries. I outline the mental model account as the most promising account since it best incorporates the findings of cognitive science. I conclude with two issues that the account needs to resolve and the role cognitive science can play in this.